In this paper we present the ERPEL approach towards executing on-the-fly e-business transactions between semantically enabled ERP systems. By on-the-fly e-business transactions we understand transactions that are conducted between companies, that are not yet in a partnership and dynamically find each other to engage in e-business transactions. Finding an appropriate business partner requires to know his business capabilities or in other words which products or services he offers. For this purpose, we develop a seamless integration of the product portfolios, held in the ERP systems, into the ERPEL registry. A search in the registry has to disclose the technical capabilities of a potential business partner to ensure interoperability. Overloaded business document standards and a variety of different communication protocols hamper an effective communication between enterprises. Thus, ERPEL follows a bottom-up approach starting from core documents with well-defined extension mechanisms. Furthermore, ERPEL comes with a default communication protocol specifically targeting SMEs. These unambiguous specifications allow the development of business service interfaces (BSI) that are integrated into the ERP systems.